The Binary pressure-volume-temperature behavior of Trihexyl(tetradecyl)phosphonium bis(trifluoromethanessulfonyl)imide in scCO2

Using a variable volume high-pressure view cell the binary mixture of Trihexyl(tetradecyl)phosphonium bis(trifluoromethanessulfonyl)imide in scCO2 was studied at molar fractions of 0.100 and 0.200 at temperature ranges of 308.15 - 343.15 K in increments of 5 Kelvin. Pressure (P) was record as a function of volume (V) while temperature was kept constant. The obtained PV-diagram is of similar shape to a single compound PV-diagram that is undergoing a phase transition. Specifically, the PV-diagram displays a region of nearly constant pressure before a sharp rise in pressure occurs as volume is further decreased. We associate the flat region in the PV-diagram with the absorption of CO2 into the ionic liquid phase. Thus the sharp rise in pressure occurs when the ionic liquid is saturated with CO2, and the PV-diagram reveals the saturation pressure.